1. Field of the Invention
This invention relates to an acrylic resin composition for coating metallic materials. More particularly it relates to the above composition obtained by copolymerizing specified acrylic acid esters or methacrylic acid esters, vinyl group-containing polysiloxane and vinyl group-containing silane compound each in a specified proportion.
This invention further relates to a decorative stainless steel piece coated with a modified acrylic resin. More particularly it relates to a decorative stainless steel piece coated with a coating material comprising a modified resin as an active ingredient obtained by copolymerizing an acrylic acid ester or a methacrylic acid ester and further as modifying monomers, a vinyl group-containing alkoxysilane, a vinyl group-containing polysiloxane and a hydroxyl group or epoxy group-containing acrylic acid ester or methacrylic acid ester.
2. Description of the Prior Art
Known thermoset acrylic resin compositions have been broadly used as coating material for various metals such as iron, aluminum, copper and stainless steel since the compositions afford a coating which is superior in luster, transparency, hardness, weather resistance, chemical resistance and other properties. However, the coating therefrom has an insufficient adhesion to metals; hence it is impossible to endure such a forming processing as bending processing through 0.degree.-2.degree. to 180.degree.. In order to impart such a bending resistance to the coating, it is necessary to blend an agent for imparting bending resistance to the thermoset acrylic resin composition. However, such a blending is accompanied with reduction in at least one of the physical properties such as hardness, chemical resistance, hot water resistance and other properties of the above coating. Thus, in order to avoid such reduction in physical properties and yet obtain a bending-processed, formed product coated with a thermoset acrylic resin composition, it is the present status that the bending-processed, formed product is post-coated with the resin composition.
However, if a coating material (a thermoset acrylic resin composition) is present which endures the above bending processing after coated, then it is possible to produce various fabricated products such as domestic appliances, office machines, building materials, etc. by the use of the so-called precoat sheet obtained by coating such a coating material onto metallic sheets. When such a precoat sheet is utilized, it is possible to remove technical difficulties at the time of coating, make the operational environment non-pollutitive and effect energy-saving, as compared with the case where individual formed products are coated; hence the above coating material which endures the bending processing has been desired.
Further, stainless steel materials, particularly stainless steel sheet, steel band, steel pipe, etc. surface-adjusted by BA (Bright Annealing), buffing, hairline polishing, etc. so as to retain their planished surfaces are characterized by endurability and metallic luster; hence these forming-processed products have been broadly used for interior and exterior parts for automobiles using trim, emblem, stainless foil, etc. for automobiles, interior and exterior building materials, furnitures, domestic appliances, etc. However, such stainless steel materials even if surface-adjusted, have raised such problems that the products are liable to cause rust or contamination, and the shade of the steel materials is limited only to the color of the stainless steel itself whereby they are restricted in the aspect of decorative properties.
For the purpose of decoration, rust prevention and contamination prevention of stainless steel materials, the materials sometimes are coated with an acrylic resin paint while making the most of the metallic luster of stainless steel. However, in the case where the coating formed from such a paint is required to have transparency and high hardness, instead softness and adhesion are sacrificed; thus when such a stainless steel material having a high hardness coating is subjected to forming such as press processing or roll processing, it raises such drawbacks that cracks occur on the coating or the coating peels off. Further, since such a coating is insufficient in salt resistance, alkali resistance and weather resistance, the uses of stainless steel materials having the high hardness acrylic resin coating have been restricted to indoor uses where the quantity of UV light is small.
As to the coloration of the surface of stainless steel materials, there is a method of forming a coating having a thickness of from 500 to 10000 .ANG. by way of anodic oxidation on the surface of the materials, to develop color on the surface through interference of natural light and reflected light (which method will hereinafter be abbreviated to "oxidation method"). However, the steel materials according to this color development method have the following drawbacks: discoloration of the processed surface of stainless steel materials, change in color tone depending on the view direction or adhesion of oil or the like and high production cost due to the treating technique. Thus this method has been applied only to extremely restricted uses. Accordingly, it has been practically very difficult to effect a transparent coloration on the surface of stainless steel material while retaining the metallic luster of the materials thereon and at the same time impart rust resistance.
In view of the foregoing technical situations, the present inventors have made extensive research in order to find a thermoset acrylic resin composition having superior forming processability after coated, and as a result have found that copolymer compositions obtained by subjecting to radical copolymerization, (a) an alkyl acrylate or an alkyl methacrylate, (b) a hydroxyl group- or epoxy group-containing acrylic acid ester, (c), a vinyl group-containing polysiloxane and (d) a vinyl group-containing silane compound, each having a definite range of carbon atoms and a definite proportion are suitable to the above-mentioned objects.
Further the present inventors have made extensive research in order to solve the problems of the prior art relative to stainless steel materials, and as a result have found that when a coating material comprising a silicone resin-modified acrylic resin as an active ingredient is coated on stainless steel materials, followed by baking, then there is obtained a siloxane bond-containing resin coating on the surface of the materials. Further it has been found that this coating does not have the above various drawbacks due to conventional acrylic resin coating materials; it is possible to blend a pigment which can bring about a desired coloration; and there is no defect of the above coating by way of anodic oxidization.
As is apparent from the foregoing, an object of the present invention is to provide a thermoset acrylic resin composition for coating metals which causes neither peeling-off nor blushing due to bending processing and is usable for coated metal sheets.
Another object of the present invention is to provide a decorative stainless steel piece coated with a modified acrylic resin, having a superior colorability and endurability.